U.S. patent application number 11/629950 was filed with the patent office on 2007-08-09 for double-side polishing carrier and fabrication method thereof.
This patent application is currently assigned to Komatsu Denshi Kinzoku Kabushiki Kaisha. Invention is credited to Yukio Oono, Yuuji Sugimoto, Kenji Yamashita.
Application Number | 20070184662 11/629950 |
Document ID | / |
Family ID | 35781794 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070184662 |
Kind Code |
A1 |
Yamashita; Kenji ; et
al. |
August 9, 2007 |
Double-side polishing carrier and fabrication method thereof
Abstract
The carrier (10) for double-side polishing has a base material
10a the material of which is stainless steel (SUS) , for example,
as is before, and the base material 10a is coated with a coating
layer 10b of a material having a hardness higher than that of the
base material 10a. The coating layer 10b is desirably coated
uniformly without variations in thickness and not warped easily,
and the material for the coating layer 10b of the double-side
polishing carrier 10 is desirably any one selected from
diamond-like carbon, a nitride film, a sapphire film and a titanium
nitride film. For production of the double-side polishing carrier
10, a double-side polishing carrier 10' having been used for
polishing is prepared first. The used carrier 10' is coated with
the coating layer 10b. The invention can suppress the progress of
abrasion of the double-side polishing carrier, and can provide
satisfactory thickness accuracy, film thickness distribution
accuracy, and surface roughness.
Inventors: |
Yamashita; Kenji; (Kanagawa,
JP) ; Oono; Yukio; (Kanagawa, JP) ; Sugimoto;
Yuuji; (Kanagawa, JP) |
Correspondence
Address: |
WELSH & KATZ, LTD
120 S RIVERSIDE PLAZA
22ND FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
Komatsu Denshi Kinzoku Kabushiki
Kaisha
25-1, Shinomiya 3-chome, Kiratsuka-shi
Kanagawa
JP
254-0014
|
Family ID: |
35781794 |
Appl. No.: |
11/629950 |
Filed: |
June 23, 2005 |
PCT Filed: |
June 23, 2005 |
PCT NO: |
PCT/JP05/11548 |
371 Date: |
December 18, 2006 |
Current U.S.
Class: |
438/692 ;
156/345.12; 216/88 |
Current CPC
Class: |
B24B 37/28 20130101 |
Class at
Publication: |
438/692 ;
156/345.12; 216/088 |
International
Class: |
C03C 15/00 20060101
C03C015/00; H01L 21/306 20060101 H01L021/306; B44C 1/22 20060101
B44C001/22; H01L 21/302 20060101 H01L021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2004 |
JP |
2004-185190 |
Claims
1. A double-side polishing carrier which is used for a double-side
polishing machine for simultaneously polishing both sides of a
subject to be polished and which holds the subject to be polished,
wherein: the carrier is coated with a material having hardness
higher than that of a base material for the double-side polishing
carrier.
2. The double-side polishing carrier according to claim 1, wherein
the material for coating the double-side polishing carrier is any
of diamond-like carbon, a nitride film, a sapphire film and a
titanium nitride film.
3. The double-side polishing carrier according to claim 1, wherein
the double-side polishing carrier has a coated thickness of 20
.mu.m or less.
4. The double-side polishing carrier according to claim 1, wherein
the coated surface of the double-side polishing carrier has a
roughness of 0.3 .mu.m or less.
5. The double-side polishing carrier according to claim 1, wherein
a double-side polishing carrier having been used for polishing is
covered with a coating.
6. A method for producing a double-side polishing carrier which is
used for a double-side polishing machine for simultaneously
polishing both sides of a subject to be polished and which holds
the subject to be polished, the method comprising: when applying a
coating to the double-side polishing carrier, coating a double-side
polishing carrier having been used for polishing with a material
having a hardness higher than that of the base material.
7. A double-side polishing carrier which is used for a double-side
polishing machine for simultaneously polishing both sides of a
subject to be polished, has a resin disposed on inner walls of
holding openings formed in a base material, and holds the subject
to be polished by the resin, wherein: a bonded portion between the
base material and the resin is coated with a material having a
hardness higher than that of the base material.
Description
TECHNICAL FIELD
[0001] The present invention relates to a double-side polishing
carrier used for double-side polishing machines and a fabrication
method thereof.
BACKGROUND ART
[0002] Silicon wafers are fabricated through individual steps
including a lapping step and a polishing step.
[0003] In the polishing step, the silicon wafer is simultaneously
polished on both sides by means of a double-side polishing machine.
In the lapping step, the both sides of the silicon wafer are
simultaneously lapped by means of a both-side lapping apparatus.
The outline of the apparatus will be described below with reference
to the double-side polishing machine as a representative.
[0004] FIG. 2 is a side view of a double-side polishing machine
100. FIG. 1 is a top view taken in the direction of arrows A of the
double-side polishing machine 100 of FIG. 2, showing a positional
relationship among double-side polishing carriers 10, silicon
wafers 1 and a lower platen 102.
[0005] The double-side polishing machine 100 comprises the
double-side polishing carriers 10 which hold peripheral edges 1c of
the silicon wafers 1 within holding openings 11 to accommodate the
silicon wafers 1 with front sides 1a and back sides 1b exposed, and
an upper platen 101 and the lower platen 102 which are respectively
mounted on the sides of the front sides 1a and the back sides 1b of
the silicon wafers 1 and have polishing cloth 103, 104 bonded to
their surfaces.
[0006] The silicon wafers 1 are housed within the holding openings
11 of the double-side polishing carriers 10, and the upper platen
101 and the lower platen 102 are moved toward the silicon wafers 1.
Thus, the polishing cloth 103, 104 are pushed against the front
sides 1a and the back sides 1b of the silicon wafers 1, the
double-side polishing carriers 10, the upper platen 101 and the
lower platen 102 are relatively rotated in opposite directions
while supplying a polishing slurry between the front sides 1a of
the silicon wafers 1 and the polishing cloth 103 of the upper
platen 101, and between the back sides 1b of the silicon wafer 1
and the polishing cloth 104 of the lower platen 102. As a result,
the front sides 1a and the back sides 1b of the silicon wafers 1
are respectively polished for a prescribed polishing volume so as
to have a mirror-finished state.
[0007] The double-side polishing carriers 10 have, for example, six
holding openings 11 and polish six silicon wafers 1
simultaneously.
[0008] The polishing cloth 103, 104 are pushed against not only the
both sides of the silicon wafers 1 but also the both sides of the
double-side polishing carriers 10. Therefore, the abrasion of the
double-side polishing carriers 10 progresses with the increase of
the polishing time, and the double-side polishing carriers 10 used
for polishing for a prescribed time period or prescribed times are
replaced with new double-side polishing carriers 10.
[0009] Material for the double-side polishing carrier 10 is
generally stainless steel.
[0010] But, the double-side polishing carriers 10 made of stainless
steel have low thickness accuracy and are variable in thickness.
Therefore, the individual silicon wafers 1 which are finished by
the individual double-side polishing carriers 10 have a
disadvantage that their flatness is variable. Besides, there is a
problem that the double-side polishing carriers 10 are abraded
quickly. Therefore, there is a problem that the silicon wafers 1
are variable in flatness depending on the progress of the abrasion
of the double-side polishing carriers 10, so that they cannot be
provided with stable flatness.
[0011] There is also a problem that where the double-side polishing
carriers 10 are worn, metal powder produced as a result causes
metal contamination of the silicon wafers 1. And, there is another
problem that where the double-side polishing carriers 10 are worn,
the metal powder produced as a result causes scratches on the
surfaces of the silicon wafers 1. Because the double-side polishing
carriers 10 are worn quickly, a replacement cycle of the
double-side polishing carriers 10 is short, resulting in high
cost.
[0012] Besides, the front sides of the double-side polishing
carriers 10 have high roughness and a high a friction coefficient,
so that the polishing cloth 103, 104 which are pushed against the
double-side polishing carriers 10 and rotated are also worn
quickly. Therefore, the replacement cycle of the polishing cloth
103, 104 becomes short, resulting in high cost.
[0013] Patent Literature 1 describes an invention that the front
side of a metal carrier is coated with a resin.
[0014] Patent Literature 2 describes an invention that a carrier is
configured of a laminated plate having carbon fiber impregnated
with a resin.
[0015] Patent Literature 3 describes an invention that an outer
peripheral gear portion of a carrier to which a mechanical load is
applied is configured of a metal material, the front side is coated
with a resin, and the remaining inside area is configured of a
resin material.
[0016] Recently, it is particularly necessary to produce an
electron device having line widths equal to or less than 0.13
.mu.m. To obtain a silicon wafer suitable for production of such an
electron device, it is demanded to prepare a silicon wafer having
flatness, which is referred to as SFQR, equal to or less than the
line widths possessed by the electron device.
[0017] The final flatness of the silicon wafer is formed by a
polishing process. To produce a silicon wafer having highly
accurate flatness, a device and method for polishing the front and
back sides of the silicon wafer simultaneously are used.
[0018] In a case where a silicon wafer having highly accurate
flatness is produced by the above so-called double-side polishing,
the thickness of the carrier for holding the silicon wafer when
polishing is important.
[0019] For example, Patent Literature 4 describes that a silicon
wafer having highly accurate flatness can be obtained by setting
the final thickness of the silicon wafer to be 2 to 20 .mu.m larger
than the carrier thickness.
[0020] Patent Literatures 5 and 6 describe that a silicon wafer
having highly accurate flatness can be obtained by setting the
peripheral part of a carrier for holding the silicon wafer to have
thickness equal to or slightly larger than the final thickness of
the silicon wafer.
[0021] Thus, a range of carrier thickness required is variable
depending on the polishing conditions, but it is required to set
the carrier thickness or its thickness in part to a particular size
with high accuracy in order to obtain a silicon wafer having highly
accurate flatness. As described above, it is necessary to improve
the accuracy of the carrier thickness in order to obtain particular
thickness with high accuracy so as to realize a silicon wafer
having highly accurate flatness.
[0022] The polishing applies a heavy load to inner walls 1a of
holding openings 11 formed in a base material 10a of the
double-side polishing carriers 10 and edge surfaces 1c of the
silicon wafers 1. Therefore, the edge surfaces 1c of the silicon
wafers 1 might be damaged. In order to prevent the silicon wafers 1
from being damaged, a resin insert for absorbing a load may be
fitted in the holding openings 11.
[0023] FIG. 7 is a plan view showing a conventional state that a
resin is fitted into a holding opening.
[0024] In order to prevent a resin insert 15 from dislocating or
corotating, wedges 10b are formed on the inner wall 1a of the base
material 11a, and wedges 15b are also formed on an outer side wall
15a of the resin insert 15. Wedges 10c and the wedges 15b are
mutually engaged to fix the resin insert 15 to the base material
10a.
[Patent Literature 1]
[0025] Japanese Utility Model Application Laid-Open Publication No.
Sho 58-4349 [Patent Literature 2] [0026] Japanese Patent
Application Laid-Open Publication No. Sho 58-143954 [Patent
Literature 3] [0027] Japanese Patent Application Laid-Open
Publication No. Hei 10-329013 [Patent Literature 4] [0028] Japanese
Patent No. 3400765 [Patent Literature 5] [0029] Japanese Patent
Application Laid-Open Publication No. Hei 11-254305 [0030] [Patent
Literature 6] [0031] Japanese Patent Application Laid-Open
Publication No. 2003-19660
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0032] According to the prior arts described in the Patent
Literatures 1 through 3, the carrier has the front side entirely or
partly formed of a resin, so that production of metal powder
associated with the abrasion of the double-side polishing carrier
can be suppressed. Thus, the occurrence of metal contamination or
scratches resulting from the production of the metal powder can be
prevented.
[0033] But, in a case where the carrier surface is simply
configured of a resin, an abrasion speed is equal to or higher than
that of a metal carrier, and a conventional problem that the
replacement cycle of the carrier is short could not be remedied.
And, where the carrier surface is simply coated with the resin,
sufficient thickness accuracy, film thickness distribution accuracy
and surface roughness cannot be obtained, the flatness of the
silicon wafer cannot be obtained stably, and the replacement cycle
of the polishing cloth cannot be prevented from becoming short.
[0034] The present invention has been made in view of the above
circumstances and provides a double-side polishing carrier of which
abrasion can be suppressed from progressing, and satisfactory
thickness accuracy, film thickness distribution accuracy and
surface roughness.
MEANS FOR SOLVING THE PROBLEMS
[0035] A first aspect is a double-side polishing carrier which is
used for a double-side polishing machine for simultaneously
polishing both sides of a subject to be polished and which holds
the subject to be polished, wherein:
[0036] the carrier is coated with a material having hardness higher
than that of a base material for the double-side polishing
carrier.
[0037] A second aspect relates to the first aspect, wherein the
material for coating the double-side polishing carrier is any of
diamond-like carbon, a nitride film, a sapphire film and a titanium
nitride film.
[0038] A third aspect relates to the first aspect or the second
aspect, wherein the double-side polishing carrier has a coated
thickness of 20 .mu.m or less.
[0039] A fourth aspect relates to the first aspect, the second
aspect or the third aspect, wherein the coated surface of the
double-side polishing carrier has roughness of 0.3 .mu.m or
less.
[0040] A fifth aspect relates to the first aspect, the second
aspect, the third aspect or the fourth aspect, wherein a
double-side polishing carrier having been used for polishing is
covered with a coating.
[0041] A sixth aspect relates to a method for producing a
double-side polishing carrier which is used for a double-side
polishing machine for simultaneously polishing both sides of a
subject to be polished and which holds the subject to be polished,
the method comprising:
[0042] when applying a coating to the double-side polishing
carrier, coating a double-side polishing carrier having been used
for polishing with a material having a hardness higher than that of
the base material.
[0043] The double-side polishing carrier 10 of the first aspect has
stainless steel (SUS) for the base material 10a in the same manner
as prior art as shown in FIG. 4, and the base material 10a is
coated with a coating layer 10b of material having hardness higher
than that of the base material 10a.
[0044] The coating layer 10b is desirably formed uniformly without
variations in thickness and not warped easily. The material for the
coating layer 10b of the double-side polishing carrier 10 is
desirably any of diamond-like carbon, a nitride film, a sapphire
film and a titanium nitride film. Among them, the diamond-like
carbon is particularly desirable because it is lightweight (the
second aspect).
[0045] The coating layer 10b of the double-side polishing carrier
10 desirably has a thickness of 20 .mu.m or less (the third
aspect).
[0046] The surface roughness of the double-side polishing carrier
10, namely the surface roughness of the coating layer 10b, is
desirably, for example, 0.3 .mu.m or less for Ra (the fourth
aspect).
[0047] Where the silicon wafers 1 are polished by the
above-described double-side polishing carriers 10, the double-side
polishing carriers 10 have high thickness accuracy and variations
in thickness of the individual carriers become small, variations in
flatness of the individual silicon wafers 1 finished by the
individual double-side polishing carriers 10 are reduced, and
stable flatness can be obtained. Besides, the progress of the
abrasion of the double-side polishing carriers 10 becomes slow,
variations in flatness of the individual silicon wafers 1 obtained
depending on a lapse of time is decreased, and stable flatness can
be obtained.
[0048] And, the production of metal powder of copper, iron, chrome
or the like associated with the abrasion of the double-side
polishing carriers 10 is substantially eliminated, and metal
contamination because of the intrusion of copper into the bulk of
the silicon wafers 1 is substantially prevented from occurring.
And, the production of metal powder associated with the abrasion of
the double-side polishing carriers 10 is substantially eliminated,
and the surfaces of the silicon wafer 1 become substantially free
from a scratch.
[0049] The progress of the abrasion of the double-side polishing
carriers 10 becomes slow, the replacement cycle of the double-side
polishing carriers 10 becomes long, and the cost is reduced.
[0050] Besides, the surface roughness of the double-side polishing
carriers 10 is low and a friction coefficient becomes low, so that
the abrasion of the polishing cloth 103, 104 which are pushed
against the double-side polishing carriers 10 and rotated becomes
slow. Therefore, the replacement cycle of the polishing cloth 103,
104 becomes long, and the cost is reduced.
[0051] To conduct the method for producing the double-side
polishing carrier 10 of the sixth aspect, a double-side polishing
carrier 10' which was used for polishing is prepared. The used
double-side polishing carrier 10' may be a carrier which does not
have the coating layer 10b formed of stainless steel in the same
manner as the prior art or may be a carrier on which the
above-described coating layer 10b is formed.
[0052] Then, the used carrier 10' is coated with the coating layer
10b.
[0053] When the double-side polishing carrier 10 is produced by the
above production method, the production cost per silicon wafer can
be reduced considerably because the used carrier is reused.
[0054] A seventh aspect relates to a double-side polishing carrier
which is used for a double-side polishing machine for
simultaneously polishing both sides of a subject to be polished,
has a resin disposed on inner walls of holding openings formed in a
base material, and holds the subject to be polished by the resin,
wherein:
[0055] a bonded portion between the base material and the resin is
coated with a material having a hardness higher than that of the
base material.
[0056] As shown in FIG. 7, to fix the resin insert 15 to the base
material 10a of the double-side polishing carrier 10, it is
generally necessary to dispose a peculiar shape such as the wedges
10c or the wedges 15b on the inner wall 11a of the holding openings
11 or the outer side wall 15a of the resin insert 15 formed in the
base material 10a. To form such a shape, it is necessary to
increase the fabrication works of the base material 10a and the
resin insert 15, but there are problems that manufacturing
efficiency of the base material 10a and the resin insert 15 lowers,
and the production cost increases.
[0057] As shown in FIG. 8, the seventh aspect has the base material
10a and a resin 20 coated with a coating layer 21 of a material
having hardness higher than that of the base material 10a. In other
words, the coating layer 21 covers a bonded portion 22 between the
base material 10a and the resin insert 20. The resin insert 20 is
fixed to the base material 10a with the coating layer 21.
Therefore, the same effect as that provided by the first aspect can
be obtained according to the seventh aspect, and the fabrication of
the base material and the resin insert is facilitated because the
base material and the resin insert do not require the wedges. Thus,
the manufacturing efficiency of the base material and the resin
insert is improved, and the production cost is reduced. And, damage
to the silicon wafer is decreased because the silicon wafer is held
by the resin insert.
BEST MODE FOR CARRYING OUT THE INVENTION
[0058] A double-side polishing carrier according to the present
invention will be described with reference to the drawings. It is
assumed in the embodiments that silicon wafers are polished by
means of a double-side polishing carrier. It should be understood
that "polishing" used through the specification includes a meaning
of lapping, and the "double-side polishing carrier" is used as a
double-side polishing carrier to be used for a double-side
polishing machine in the polishing step, and also means a carrier
used for a double-side polishing machine (both-side lapping
apparatus) in the lapping step.
[0059] The double-side polishing carrier of the invention can also
be used to polish not only the silicon wafers but also other
semiconductor wafers of gallium arsenide and the like.
[0060] FIG. 2 is a side view of the double-side polishing machine
100. FIG. 1 is a top view taken in the direction of arrows A of the
double-side polishing machine 100 of FIG. 2, showing a positional
relationship among the double-side polishing carriers 10, the
silicon wafers 1 and the lower platen 102.
[0061] The double-side polishing machine 100 generally comprises
the double-side polishing carriers 10 which hold the peripheral
edges 1c of the silicon wafers 1 within the holding openings 11 to
accommodate the silicon wafers 1 with the front sides 1a and the
back sides 1b exposed, and the upper platen 101 and the lower
platen 102 which are respectively disposed on the sides of the
front sides 1a and the back sides 1b of the silicon wafers 1 and
have the polishing cloth 103, 104 bonded to their front sides.
[0062] A cooling water passage 106 is formed in the upper platen
101, and a cooling water passage 108 is also formed in the lower
platen 102. Passages for polishing slurry 107 which are
communicated with the surface of the polishing cloth 103 are formed
in the upper platen 101, and passages for polishing slurry (not
shown) which are communicated with the surface of the polishing
cloth 104 are also formed in the lower platen 102.
[0063] FIG. 3 shows a magnified form of the double-side polishing
carrier 10 of FIG. 1.
[0064] Referring to FIG. 3 in addition to FIG. 1 and FIG. 2, the
double-side polishing carrier 10 is formed to have a disk-like
shape and has, for example, six holding openings 11 formed to
accommodate the silicon wafers 1 at equal intervals in the
circumferential direction. Gear teeth 12 (planetary gear) are
formed along the outer periphery of the double-side polishing
carrier 10, engaged with a sun gear 102a formed at the center of
the lower platen 102, and also engaged with an inside gearwheel 105
which is disposed along the outer periphery of the lower platen
102. Five double-side polishing carriers 10 are disposed at equal
intervals in the circumferential direction of the lower platen 102
with the sun gear 102a at the center.
[0065] In a case where the silicon wafers 1 are polished, the
silicon wafers 1 are put in the holding openings 11 of the
double-side polishing carriers 10. The upper platen 101 and the
lower platen 102 are moved toward the silicon wafers 1, so that the
polishing cloth 103, 104 are respectively pushed against the front
sides 1a and the back sides 1b of the silicon wafers 1. And, the
double-side polishing carriers 10, the upper platen 101 and the
lower platen 102 are relatively rotated in opposite directions
while supplying the polishing slurry between the front sides 1a of
the silicon wafers 1 and the polishing cloth 103 of the upper
platen 101 and between the back sides 1b of the silicon wafers 1
and the polishing cloth 104 of the lower platen 102.
[0066] The double-side polishing carriers 10 rotate on their axes
in the direction indicated by arrow B in FIG. 1 and also rotate in
the circumferential direction of the sun gear 102a as indicated by
arrow C.
[0067] Thus, the front sides 1a and the back sides 1b of the
silicon wafers 1 are respectively polished for a prescribed
polishing volume to have a mirror polished state. As described
above, the double-side polishing carriers 10 each are formed to
have, for example, six holding openings 11, so that the single
double-side polishing carrier 10 can polish six silicon wafers 1
simultaneously.
[0068] FIG. 4 shows a sectional view of the double-side polishing
carrier 10.
[0069] As shown in FIG. 4, the double-side polishing carrier 10 has
stainless steel (SUS) as the material for the base material 10a in
the same way as the prior art, and the base material 10a is covered
with a coating layer 10b of a material having hardness higher than
that of the base material 10a.
[0070] The coating layer 10b is desirably coated uniformly without
variations in thickness and not warped easily. And, the material
for the coating layer 10b of the double-side polishing carrier 10
is desirably any of diamond-like carbon, a nitride film, a sapphire
film, and a titanium nitride film. Among them, the diamond-like
carbon is especially desirable because it is lightweight and
provides good uniform coating.
[0071] The material for the base material 10a of the double-side
polishing carrier 10 may be metal or resin assumed in this
embodiment.
[0072] In a case where the base material 10a of the double-side
polishing carrier 10 is metal, it may be stainless steel (SUS) as
described above or may be steel. Specific material for the base
material 10a may be SK material, 18-8 stainless steel, Cr steel,
super Cr steel or the like. When the base material 10a of the
double-side polishing carrier 10 is metal, it may be entirely
formed of metal or partly formed of a resin. For example, in the
double-side polishing carrier 10, the inner peripheral surfaces 1 a
of the holding openings 11, namely the contact surfaces 11a with
the edge surfaces 1c of the silicon wafers 1, may be formed of the
resin (see FIG. 3).
[0073] When the base material 10a of the double-side polishing
carrier 10 is a resin, the coating layer 10b of a different
material may be formed on the resin, and the coating layer 10b of
the same material as that of the resin of the base material 10a may
be formed.
[0074] Flatness of the silicon wafer 1 depends on the thickness
accuracy of the carrier 10. The thickness accuracy of the carrier
10 depends on the thickness accuracy in the production process of
the carrier 10 and the thickness accuracy depending on thermal
expansion during the polishing process. As to the thickness
accuracy of the carrier 10, the carrier 10 formed of the base
material 10a which is a resin is superior to the carrier 10 formed
of the base material 10a which is metal. Meanwhile, as to the metal
contamination to the silicon wafers 1, the carrier 10 formed of the
base material 10a which is a resin is superior.
[0075] The coating layer 10b of the double-side polishing carrier
10 is desirably 20 .mu.m or less in thickness. It is because the
carrier 10 is warped considerably as the thickness of the coating
layer 10b increases.
[0076] Surface roughness of the double-side polishing carrier 10,
namely the surface roughness of the coating layer 10b , is
desirably, for example, 0.3 .mu.m or less for Ra. It is because if
the surface roughness of the coating layer 10b is excessively
large, the polishing cloth 103, 104 have a shortened life.
[0077] In a case where the double-side polishing carrier 10 is
coated with the coating layer 10b, at least portions excepting the
contact surfaces 11a which are in contact with the edge surfaces 1c
of the silicon wafers in the holding openings 11 are coated, and
the contact surfaces 11a are desirably coated with a resin which
does not apply a load to the edge surfaces 1c of the silicon
wafers.
[0078] The double-side polishing carrier 10 may be coated entirely,
only one side may be coated, or only the portions excepting the
gear teeth 12 may be coated.
[0079] Where the above-described double-side polishing carriers 10
are used to polish the silicon wafers 1, stable flatness can be
obtained because the double-side polishing carriers 10 have highly
accurate thickness, variations in thickness of the individual
carriers become small, and variations in flatness of the individual
silicon wafers 1 finished by the individual double-side polishing
carriers 10 become small. Besides, the progress of the abrasion of
the double-side polishing carriers 10 become slow, variations in
flatness of the individual silicon wafers 1 obtained with a lapse
of time become small, and stable flatness can be obtained.
[0080] Generation of metal powder such as copper, iron or chrome
associated with the abrasion of the double-side polishing carrier
10 is substantially eliminated, and metal contamination due to
migration of copper into the bulk of the silicon wafers 1 hardly
occurs. And, generation of metal powder associated with the
abrasion of the double-side polishing carrier 10 is substantially
eliminated, and scratches hardly occur on the surface of the
silicon wafer 1.
[0081] The progress of the abrasion of the double-side polishing
carrier 10 is delayed, the replacement cycle of the double-side
polishing carriers 10 is extended, and the cost can be reduced.
[0082] Besides, the surface roughness of the double-side polishing
carriers 10 is lowered, a friction coefficient is lowered, and the
abrasion of the polishing cloth 103, 104 which are pushed against
the double-side polishing carriers 10 and rotated is delayed.
Therefore, the replacement cycle of the polishing cloth 103, 104 is
extended and the cost can be reduced.
[0083] Examples (test results) which prove the above-described
effects are shown in FIG. 5 and FIG. 6.
[0084] FIG. 5B shows variations in flatness SFQR (.mu.m) of the
silicon wafers 1 polished by using the double-side polishing
carriers 10 of the embodiment described above. The horizontal axis
of FIG. 5B represents the flatness SFQR (.mu.m), and the vertical
axis represents quantity N of the silicon wafers 1. A comparative
example of using conventional double-side polishing carriers 10 not
coated with the coating layer 10b is shown in FIG. 5A.
[0085] The polishing conditions are as follows. [0086] Material
wafer: P type<100> 0.005 to 10.OMEGA. [0087] Polishing
machine: Double-side polishing machine [0088] Polishing cloth :
Nonwoven type, hardness 80 (Asker C hardness) [0089] Polishing
slurry: Colloidal silica (pH=11) [0090] Polishing load: 120
g/cm.sup.2 [0091] Carrier: .phi.=720 mm, t=700 .mu.m, .phi.200 mm
(dia.) six wafers loaded
[0092] Flatness of the silicon wafer 1 was measured by ADE9700.
[0093] It is apparent by comparing FIG. 5A and FIG. 5B that the
flatness of the wafers obtained by using the conventional
double-side polishing carrier 10 is deteriorated because the
carriers 10 are abraded with the increase in the number of times of
using the carriers, so that variations in flatness of the wafers
are large with plural polishing batches (FIG. 5A; Ave. 0.071 .mu.m,
Std. 0.05). Meanwhile, it was confirmed that when the double-side
polishing carriers 10 of this embodiment were used, the abrasion of
the carriers 10 associated with the increase in the number of times
of using the carriers could not be confirmed at all, and good
flatness of the wafers could be kept even with plural polishing
batches (FIG. 5B; Ave. 0.053 .mu.m, Std. 0.02).
[0094] FIG. 6 is a graph showing comparison between an abraded
amount of the double-side polishing carrier 10 of the embodiment
and that of a conventional double-side polishing carrier 10. FIG. 6
indicates the number of polishing batches along the horizontal axis
and the accumulated value (.mu.m) of abraded amounts of the carrier
along the vertical axis. In FIG. 6, mark .tangle-solidup. indicates
plots of the accumulated value (.mu.m) of abraded amounts of the
carrier 10 of stainless steel, which is not coated with the coating
layer 10b, of the comparative example, and mark .circle-solid.
indicates plots of the accumulated value of abraded amounts of the
carrier 10 of the embodiment having the entire surface of the base
material 10a of stainless steel coated with the coating layer 10b
of diamond-like carbon.
[0095] The polishing conditions are as follows: [0096] Polishing
machine: Double-side polishing machine [0097] Polishing cloth:
Nonwoven type, hardness 80 (Asker C hardness) [0098] Polishing
slurry: Colloidal silica (pH=11) [0099] Polishing load: 120
g/cm.sup.2 [0100] Polished and removed amount: 15 .mu.m
[0101] The wafer 1 to be polished has a size of .phi.200 mm
(dia.).
[0102] The thickness of the carrier 10 was measured with a
micrometer having a representation unit of 1 .mu.m.
[0103] As apparent from FIG. 6, it was confirmed that the
conventional double-side polishing carrier 10 used as comparative
example was abraded more conspicuously with increasing polishing
batches, and where the double-side polishing carrier 10 of this
embodiment was used, the abrasion of the carrier associated with
the increase of the polishing batches was so small that it could
not be confirmed by using a micrometer having a representation unit
of about 1 .mu.m.
[0104] The wafer having a diameter of 200 mm was used in the
examples shown in FIG. 5 and FIG. 6, but the same effects can also
be obtained by using wafers having various sizes such as wafers
having a diameter of 300 mm.
[0105] Then, an example of the method for producing the double-side
polishing carrier 10 will be described.
[0106] A double-side polishing carrier 10' having been used for
polishing is prepared. The used double-side polishing carrier 10'
may be a carrier formed of the same stainless steel as in the prior
art and not having the coating layer 10b or may be a carrier having
the above-described coating layer 10b.
[0107] Then, the entire surface of the used carrier 10' is coated
with the above-described coating layer 10b excepting the contact
surface 11a of the holding opening 11.
[0108] The contact surface 11a of the holding opening 11 of the
used carrier 10 ' is coated with a resin.
[0109] In a case where the double-side polishing carrier 10 is
produced according to the above described production method, the
production cost per silicon wafer can be reduced considerably
because the used carrier is reused. Besides, the used carrier 10'
has a mirror-finished surface because of its previous use in the
polishing step. Thus, it has an advantage that the coating layer
10b can be coated easily.
[0110] FIG. 8A to FIG. 8C show sectional views of the double-side
polishing carrier of the embodiment that a resin insert is fitted
into a holding opening. It is assumed that the holding opening is
on the right side in FIG. 8A to FIG. 8C. FIG. 9 is a plan view
showing a state of the embodiment that the resin insert is fitted
into the holding opening.
[0111] Similar to FIG. 4, the double-side polishing carrier 10 has
the base material 10a which is formed of stainless steel (SUS) in
the same way as the prior art. An annular resin insert 20 is fitted
into the holding opening 11 formed in the base material 10a. As
shown in FIG. 9, the inner wall 11a of the base material 10a and
the outer side wall 20a of the resin insert 20 have a smooth curbed
surface, and they are mutually contacted closely. As shown in FIG.
8, the base material 10a and the resin insert 20 which are mutually
contacted closely are coated with a coating layer 21 formed of a
material having hardness higher than that of the base material
10a.
[0112] The bonded portion 22 of the base material 10a and the resin
insert 20 is coated with the coating layer 21, so that the base
material 10a and the resin insert 20 become one body, and the resin
insert 20 is fixed to the base material 10a. The coating layer 21
may have a variety of forms. For example, as shown in FIG. 8A, the
coating layer 21 may cover the upper and lower sides of the base
material 10a and the upper and lower sides and inner wall of the
resin insert 20. As shown in FIG. 8B, the upper and lower sides of
the base material 10a and the upper and lower sides of the resin
insert 20 may be coated with the coating layer 21. As shown in FIG.
8C, the coating layer 21 may cover the upper and lower sides of the
base material 10a and partly cover the upper and lower sides of the
resin insert 20.
[0113] The coating layer 21 and the base material 10a of FIG. 8
will be described below though the description will partly overlap
the description of the above-described coating layer 10b and the
base material 10a.
[0114] The coating layer 21 is desirably coated uniformly without
variations in thickness and not warped easily, and the material for
the coating layer 21 of the double-side polishing carrier 10 is
desirably any one selected from diamond-like carbon, a nitride
film, a sapphire film and a titanium nitride film. Among them, the
diamond-like carbon is particularly desirable because it is
lightweight and provides a uniform film.
[0115] The material for the base material 10a of the double-side
polishing carrier 10 is desirably the metal assumed in this
example.
[0116] In a case where the base material 10a of the double-side
polishing carrier 10 is metal, the material may be stainless steel
(SUS) as described above or steel. Specific material for the base
material 10a may be SK material, 18-8 stainless steel, Cr steel,
super Cr steel or the like. Even when the base material 10a of the
double-side polishing carrier 10 is metal, the entire body may be
metal.
[0117] The material for the resin insert 20 may be a nylon resin or
the like.
[0118] The base material 10a and the resin insert 20 can be
prevented from being abraded by coating the coating layer 21 on not
only the base material 10a but also the resin insert 20 and the
bonded portion between the base material 10a and the resin insert
20. As described above, the resin insert 20 can be fixed to the
base material 10a, so that it is not necessary to form wedges or
the like on the inner wall 11a of the holding opening 11 formed in
the base material 10a and the outer side wall 20a of the resin
insert 20. Thus, it becomes easy to fabricate the base material 10a
and the resin insert 20. Damage to the silicon wafer 1 can be
reduced because the silicon wafer 1 is held by the resin insert
20.
[0119] It is desirable that the thickness of the resin insert in
the radial direction is thin. The reason will be described with
reference to FIG. 10.
[0120] FIG. 10A and FIG. 10B are sectional views of the double-side
polishing carrier of an embodiment that the resin insert is
fitted.
[0121] When polishing, the polishing cloth 104 enters a gap 30
formed between a chamfer 1d of the silicon wafer 1 and the resin
insert 20. The resin insert 20 is soft and deformed by an effect of
the polishing cloth 104 which has entered the gap 30. As shown in
FIG. 10A, a deflection amount becomes large when the thickness of
the resin insert 20 in the radial direction is large, an amount of
the polishing cloth 104 entering the gap 30 increases. Therefore,
the periphery of the chamfer 1c of the silicon wafer 1 is polished
excessively. Meanwhile, as shown in FIG. 10B, when the thickness of
the resin insert 20 in the radial direction is small, the
deflection amount becomes small, and the amount of the polishing
cloth 104 entering the gap 30 becomes small. Thus, the periphery of
the chamfer 1c of the silicon wafer 1 is prevented from being
abraded excessively.
[0122] In the above-described embodiment, it was described above
assuming that polishing was performed by the double-side polishing
machine with semiconductor wafers such as silicon wafers housed in
the double-side polishing carrier, but the subjects to be polished
which are housed in the double-side polishing carrier and polished
by the double-side polishing machine are arbitrary.
BRIEF DESCRIPTION OF THE DRAWINGS
[0123] FIG. 1 is a top view of a double-side polishing machine in
which double-side polishing carriers are incorporated.
[0124] FIG. 2 is a side view of the double-side polishing machine
in which the double-side polishing carriers are incorporated.
[0125] FIG. 3 is a magnified view of the double-side polishing
carrier shown in FIG. 1.
[0126] FIG. 4 is a sectional view of the double-side polishing
carrier.
[0127] FIG. 5A and FIG. 5B are graphs used for description of the
effects of the embodiment.
[0128] FIG. 6 is a graph used for description of the effects of the
embodiment.
[0129] FIG. 7 is a plan view showing a conventional state that a
resin is fitted into a holding opening.
[0130] FIG. 8A to FIG. 8C are sectional views of the double-side
polishing carrier of the embodiment that a resin is fitted into a
holding opening.
[0131] FIG. 9 is a plan view showing a state of an embodiment that
a resin is fitted into a holding opening.
[0132] FIG. 10A and FIG. 10B are sectional views of the double-side
polishing carrier of an embodiment that a resin insert is
fitted.
DESCRIPTION OF THE REFERENCE NUMERALS
[0133] 1 Silicon wafer [0134] 10 Double-side polishing carrier
[0135] 10a Base material [0136] 10b Coating layer [0137] 100
Double-side polishing machine
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